Researchers are one step closer to understanding the science behind near death experiences. For a study published in the journal Critical Care, Slovenian researchers found that cardiac arrest patients who reported near-death experiences—everything from flashing lights to looking down over one’s body from above—had significantly higher levels of carbon dioxide in their blood. Until now, these experiences, thought to be experienced by one in 10 people and a quarter of cardiac arrest patients, were chalked up to religion or drugs. But in the Slovenian study, these factors did not link those who cited near-death moments—11 of 52 subjects. Report author Zalika Klemenc-Ketis called the link to carbon dioxide “another piece of the puzzle,” but said that “much more work is needed” to fully understand these mysterious moments.